The present invention generally concerns goggles which are a protective glasses set usually in a flexible frame that fits snugly around the wearer's eyes' thus protecting the eyes against airborne gases and particles.
Goggles generally comprise an optical surface, designed to transmit images with minimal optical aberrations. This optical surface (hereinafter to be referred to by the term "lens") may be made of glass or various transparent plastic materials such as polycarbonate. Polycarbonate which has characteristically a high mechanical strength is usually the preferred substance for use in such lenses.
Goggles' lenses, unless designed for a specific individual, should be optically neutral, i.e. they should cause no or only very little aberrations of the transmitted image. In general, optical aberrations by lenses may be caused either by an incorrect placement of the lens in front of the eye or by inherent properties of the lens itself. To date, only plannar lenses are known to be immune of these two types of optical abberations and therefore all goggles which were hitherto available had such lenses, known also as "window lenses". A major drawback of such lenses is the fact that the field of vision through them is limited. This drawback considerably limits the applicability of goggles.
Against this, spherical lenses have a large field of vision, sometimes almost as large as the naked eye. However, all spherical lenses used to date cause considerable optical aberrations of the transmitted optical image. One source of these aberrations is intrinsic in that the dioptric of a spherical lens is relatively high, and results from the fact that such lenses have, as a rule, a relatively short focal length. For example, a concentric lens (a spherical lens in which the two surfaces have a common centre of curvature) made of polypropylene having standard design parameters such as a thickness of around 2 mm and a radius of the inner surface of about 25-30 mm, has a focal length of about 1 meter, i.e. a power of about 1 diopter. Another source of the optical abberation in such lenses results from placement errors, namely incorrect placement of the lens with respect to the eye: where the exit pupil, i.e. the eye, is located outside the lens's axis of symmetry, the optical aberrations of the transmitted image increase considerably. Since placement errors are practically unavoidable seeing that the inter-eye distance and the position of the eye with respect to the eyes' orbit, vary considerably to a very big extent between different individuals, aberrations due to placement errors are bound to occur in goggles with spherical lenses which is a serious drawback.
Some of the optical aberrations caused by spherical lenses may at times be corrected by tailor-making the lens to a specific individual.
It is the object of the present invention to provide spherical lenses for goggles suitable for use by all individuals, which transmit the optical image with little aberrations.